When Agricola's legions stormed to the north of Britain to face the tribes of Caledonia nearly 2,000 years ago, the Roman governor of Britain used exactly the same strategy as the Pentagon in Iraq. He sent his fleet ahead to spread uncertainty and terror - for which read the aerial bombardment of Baghdad - and then marched north with a highly mobile and lightly equipped army.

His son-in-law, the historian Tacitus, recorded that the Scottish tribes greatly outnumbered the Romans yet when they saw Agricola's ability to regroup his army in battle they turned and ran. By the end of the engagement Agricola had lost just 360 men, against the enemy's 10,000 casualties.

The parallels between the Roman and American actions are striking, not just in the daring tactics, the relative losses and superior organisation but also in their motivation. Agricola undertook the campaign to prevent a 'general rising of the northern nations' - ie to provide security for the region and ultimately for Rome even though it lay 1,000 miles away.

At the time the reaction to the Romans was much the same as the passion and fear inspired by the Americans today. According to Tacitus, the leader of the Caledonian forces, Calgacus, described the Romans thus: 'Pillagers of the world, they have exhausted the land by their indiscriminate plunder ... The only people on Earth to whose covetousness both riches and poverty are equally tempting. To robbery, butchering, and rapine, they give the lying name of government; they create desolation and call it peace.'

Few Arabs would have any difficulty with that if it was applied to the Americans; indeed it is precisely the kind of thing heard in mosques all over the Middle East. Most Europeans would not go that far yet this war has provoked extraordinary passions.

Pro- and anti-war sentiments stir from the depths of each personality in a way that cannot always be explained by an individual's age, class, gender or ethnic background. And those that have found certainty have not easily relinquished their conviction as events unfold. For example, the peace party has been unwilling to concede the following: the ecological disaster in the southern oil fields has not materialised; up to this point casualties have been far fewer on both sides than expected; the Arab street has not risen to threaten regimes all over the Middle East; the rapid advance across has not proved the military catastrophe so many predicted.

Equally unyielding is the enthusiasm of the hawks who have generally dismissed the destruction and loss of life as being a regrettable but necessary sacrifice on the way to a number of geostrategic goals - a new world order, greater security for Israel and America and democratic reform in the Arab world.

They have a passion for the design and execution of a plan, whatever its risks, and they tend to inflate the benefits that will accrue. For their part they do not concede these points: the plan was a gamble; no substantial evidence of the production and retention of weapons of mass destruction has yet come to light; success in Afghanistan and Iraq may lead US hawks to plan a series of ever more perilous campaigns; the long-term damage to Arab pride and the likelihood of increased terrorist attacks.

The level of feeling is unlikely to be dampened by a victory in Baghdad. For example Matthew Parris in the Spectator talked of 'his cold anger at the stupidity of it all, the awful miscalculations being made and the damage being done and feelings of useless despair of a quite personal sort'.

Last week Parris was joined by the novelists Arundhati Roy and Rachel Cusk, who wrote in the Guardian of the suffering and shame involved in the Iraq war. Roy observed: 'Operation Iraqi Freedom? I don't think so It's more like Operation Let's Run a Race, but First Let Me Break Your Knees.' Taken to its logical conclusion this means Roy objects to the war because more men from the coalition forces aren't being killed, a position which suggests more than just simple pacifism, I would suggest. Jemima Khan announced in the Independent that she was ashamed of being British, which is odd in at least one regard since British forces seem to have behaved with good judgment and impeccable restraint.

Again we should agree that neither the authenticity of these feelings nor the motives of the two principal anti-war newspapers, the Daily Mirror and the Independent , should be questioned. However, there is a hysterical note to some of the commentary and writers have paraded a moral rectitude that has never at any stage absorbed the true darkness of Saddam's regime.

This war has many more antecedents apart from Agricola's campaign on the Forth. One is particularly reminded of the daring and speed of the Israeli military in June 1967 and in October 1973, after it recovered from a surprise attack during Yom Kippur. But in other respects what we are seeing is totally new and this may account for the levels of shock and dread being voiced.

American power, restrained for so long by hesitant generals and cautious politicians, has now been welded to a strategic culture that is prepared to contemplate the loss of American lives on the way to certain goals. The unapologetically proactive approach is new and its is clear from the performance of the US military that the deadliness, organisation and speed of its forces are all considerably greater than they were in the 1991 Gulf war.

The alliance of might and ideas represent a new kind of dominance which causes equal anxiety in the Middle East and Europe, but for different reasons. The Arab states have suffered a blow to their self-esteem equivalent to that of 1967, but this time it is not Israeli tanks outflanking and outgunning Arab forces, but American armour.

The fear and helplessness that the last few weeks engender in Arabs will not die away when order is restored to Iraq. Their leaders are worried that democratic reform in Iraq will cause turmoil in neighbouring states - which, by the way, it should - while the general populations believe a victory in Iraq will make resolution of the Palestine-Israel conflict less rather than more likely.

In Europe the peace party has been inspired by some genuine pacifism but also by the offence caused to the liberal consensus and its faith in liberal institutions such as the UN. A few American hawks and a President who has almost no experience of Europe or the Middle East have brushed aside the United Nations, the prudent counsels of European leaders and the motivated qualms of the Chinese and Russians with very little obvious soul searching.

Where this leads is difficult to say, which in itself is one of causes of the unprecedented anti-American mood. At base the peace movement is fuelled by a thoroughly human fear of the unknown and it is perhaps up to the hawks to acknowledge this reality with slightly more tact than has been displayed so far. What none of us needs is the triumphalist parades of US military and diplomatic supremacy. When Agricola returned to Rome after his successful campaign in the Britain, he stole into the city by night to avoid his friends and supporters.

· Empire State, a novel by Henry Porter about a US/UK counter-terrorist operation, is published by Orion in September.